|WikiProject Chemistry||(Rated C-class, Low-importance)|
thermodynamics of eutectics
This article needs some major expansion in this area; eutectics form because of limited solubility of one component in another and thus the favourability of separating into a mixture of two phases of distinct compositions, but the article doesn't really comment on this. John Riemann Soong (talk) 12:47, 12 November 2009 (UTC)
Renaming to Eutectic system
I don't like how this article is named "eutectic point" because that is just part of the whole system. My Foundations of material science and engineering book calls it a binary eutectic alloy system, but I feel that's too complex, so I propose a rename to eutectic system. Then we can easily incorporate lots of other terms (some of which are already in the article), like eutectic composition, eutectic composition, eutectic reaction, etc. Wizard191 (talk) 00:46, 19 November 2009 (UTC)
I would just like to say that I was very impressed with this article. It explains a complicated concept clearly and concisely.
There is no Theory Explained
I agree it describes the phenomenon very well. I would like to understand why the melting point of a mixture of two substances would be lower than that of either substance individually. —Preceding unsigned comment added by 126.96.36.199 (talk) 18:05, 4 May 2010 (UTC)
- You might want to read this (through page 53). It appears that scientists don't know. Wizard191 (talk) 16:39, 6 May 2010 (UTC)
Influence of time
It might be interesting to also explain the influence of time in this process. Yes, Eutectic reaction takes place if cooling is sufficiently slow. Then the thermodynamics and free energy drive the process. Okay. But crystallization of two solid phases from a liquid is a kinetic reaction and takes time. If you cool very rapidly and get to a sufficiently low temperature while remaining in a non-crystallized structure like the liquid, then you form a metallic glass. These metallic glasses are amorphous materials with no long range crystal structure (though short range clustering is certain to occur). If the local minima of the free energy is sufficiently deep, then the amorphous structure can be stable over long periods of time at room temperature. In all cases, the discussion here leads to a new link to amorphous materials which are an interesting class of materials. —Preceding unsigned comment added by 188.8.131.52 (talk) 21:21, 12 October 2010 (UTC)
Definitions of variables
In figure 1, L, alpha, and beta are not defined. In the equation, alpha and beta are not defined. Hence it is difficult for the non-expert to glean knowledge from this article. —Preceding unsigned comment added by 184.108.40.206 (talk) 03:37, 21 March 2011 (UTC)
- if Wizard191 defined the variables in the image someone must have removed the definitions because alpha and beta are not currently defined either in the image or anywhere on the entire page. This is a major gap that needs to be corrected. I presume there is probably some relationship between alpha and A and between beta and B but it needs to be explicitly stated withing the article. Without a a clear definition of all variables the reader is left with guesswork and the article is only useful to someone already familiar with the topic. 220.127.116.11 (talk) 01:34, 9 May 2013 (UTC) Paul Carver 2013-05-08
but I'm still confused. I need something to guide me thru that phase diagram.
Say I have a chunk of metal in my crucible. It's an alloy that's 90% alpha and 10% beta (pretending the diagram is to scale and everything). We start near the bottom of the diagram and we're going straight up. It's cold cuz I just turned on the heat. So it's 'alpha + beta' - does that mean a solid solution of alpha and beta, or a nonsolution, some nonsolution composition with lumps of beta floating in alpha or something?
then it warms up, getting close to around the eutectic temperature and it magically becomes all alpha? that's what the diagram seems to say. what happened to the 10% beta? or do you mean it separates into two parts, one part is all alpha (so it follows a path more to the left) and the other part is a mix that follows a path more to the right?
Warming up more, it turns into a mixture of
- solid chunks of pure alpha
- a liquid, whatever solution of alpha and beta makes up the rest
This mixture is like a slurry? or more like honey or candle wax or chocolate? and as it warms, the viscosity decreases and finally:
The last few bits of alpha melt and it's entirely a liquid composed of 90% alpha and 10% beta.
- I think this is the correct answer, so bear with me if I'm wrong: Consider a 10% salt solution (L = brine), again assuming that the diagram is to scale and representative of the NaCl-water system. If you cool it down slowly, ice (alpha) begins to form, rejecting salt from its structure, and the salinity of the solution increases, depressing the freezing point. This means that over a range of temperatures, you have both L and alpha present. If you cool it down past zero Farenheit, all the brine will freeze, and if the ratios are right, it'll all resemble impure ice (alpha). If you manage to cool it right down, the salt ions/water molecules will begin to separate into ice (alpha) and salt (beta).
- If your salt concentration was greater (60% as per the diagram), as you cooled the solution down the solubility of salt would decrease. Salt (beta) would precipitate from the brine, corresponding to L + beta. Cool it further, and you have a mixture of salt and ice. Hope that helps. Tomásdearg92 (talk) 13:39, 8 April 2012 (UTC)
a single multiple chemical composition ??
A eutectic system is a mixture of chemical compounds or elements that has a single multiple chemical composition that solidifies...
- Fixed it myself (by looking at the history), sorry for the spam! — Preceding unsigned comment added by 18.104.22.168 (talk) 14:02, 12 November 2012 (UTC)
More detail needed on binary alloys without any eutectic point.
In the lead section, a eutectic system is defined as follows:
- A eutectic system is a mixture of chemical compounds or elements that has a single chemical composition that solidifies at a lower temperature than any other composition made up of the same ingredients.
It then says:
- Not all binary alloys have a eutectic point; for example, in the silver-gold system the melt temperature (liquidus) and freeze temperature (solidus) both increase monotonically as the mix changes from pure silver to pure gold.
The article could really use some expansion on this: why is there not a eutectic point at a composition of 100% silver and 0% gold? From the explanation and by looking at cited phase diagram, that composition seems to fit the definition of "solidifying at a lower temperature than any other composition made up of the same ingredients." Draconx (talk) 19:14, 28 November 2012 (UTC)